This paper investigates the effects of asynchronous multiple access interference (MAI) on the performance of orthogonal frequency-division multiple access (OFDMA) uplink systems in frequency-selective Rayleigh fading environments. We first analyze the MAI and its statistical characteristics using the Gaussian approximation. Then the analytical expression for the uncoded average symbol error probability (SEP) is obtained with various modulation schemes. Comparison with simulation results shows a tight agreement of the proposed analysis over a wide range of asynchronous timing errors and for various numbers of asynchronous users. Numerical examples show that when asynchronous timing errors reside within the guard interval, a performance of uncoded SEP- 10-3 can be feasible even in high dispersive environments. Furthermore, the effect of the Gaussian approximation is examined, and the performance comparison between interleaved- and block-type subcarrier allocation schemes is provided.

Future wireless systems will need to employ blind estimation to achieve better spectral efficiency. In this letter, we introduce a blind synchronization algorithm for jointly estimating timing and frequency offset in orthogonal frequency division multiplexing (OFDM) systems. The proposed estimator exploits the second-order cyclostationarity of received signals and then uses the symbol-timing and carrier frequency offset information appearing in the cyclic correlation. Because it is a blind estimator, no channel impulse response information is required. Simulations demonstrate that the proposed estimator performs at a sufficiently high level, thus indicating its suitability for use over fading channels.

We present a novel timing offset estimation method for orthogonal frequency division multiplexing(OFDM) systems. The proposed estimator is designed to avoid the ambiguity in timing offset estimation. The performance of proposed scheme is presented in terms of mean and mean-square error (MSE) sense. The simulation results show that the proposed estimator is unbiased and has significantly smaller MSE.

In this paper, we examine the performance degradation due to the imperfect channel information in orthogonal frequency division multiplexing (OFDM)-based wireless LAN (WLAN). The average effective SNR and average bit error probabilities are derived in Rayleigh fading channels.

Blind synchronization algorithm is developed for estimating jointly timing and frequency offset of OFDM signals transmitted through a frequency-selective fading channel. The proposed estimator exploits the second-order cyclostationarity of received signals. As a blind estimator, the information of impulse response of channel is not required. The performance of the estimator is evaluated through computer simulations.